Polyolefins such as polyethylene (PE) and polypropylene (PP) are light-weight and inexpensive, and have excellent physical properties and processability, and are thus used in various fields such as food packages, clothes/cosmetics/medical containers, automobile parts, communication/electrical instrument parts, civil engineering/building materials, agricultural materials and medical instruments, and occupy a very important position as general-purpose resin. In recent years, however, demand for physical properties of polyolefins has been diversified, and there is a need for polyolefins having properties absent in existing polyolefins, for example polyolefins excellent in heat resistance, polyolefins having a soft feel similar to that of soft polyvinyl chloride and polyolefins endowed with high functions such as printability, coating properties, adhesiveness and compatibility with other polar polymers.
The method of improving the physical properties of the polyolefin to confer high functions includes not only a method that involves regulating the type and molar ratio of monomers and a method that involves changing a random or block monomer sequence, but also a method of copolymerizing a polar monomer such as vinyl acetate or methacrylate with an olefin by radical polymerization and a method of copolymerizing a polar monomer such as maleic anhydride with polyolefin in the presence of a peroxide. In these methods, however, it is difficult to accurately regulate the structure of the polyolefin moiety in the resulting polymer, and there is a limit to the amount and type of the polar monomer introduced.
The known method of conferring the original excellent performance of the polyolefin by incorporation of a polyolefin component having an accurately regulated structure and simultaneously giving functions to the polyolefin by incorporation of a polar polymer component includes a method of coupling reaction of a functional group-containing polyolefin with a polar polymer and a method of producing a block or graft polymer having a polyolefin and a polar polymer bound chemically thereto by using a functional group-containing polyolefin as a macroinitiator or a macromonomer. However, these known methods are limited to block or graft polymers having one kind of polyolefin and one kind of polar polymer bound chemically thereto, and are thus insufficient to confer various physical properties and functions by combining a plurality of polyolefins and a plurality of polar polymers.
Further, it can be expected to produce the production of multi-branched polymers having various structures such as a block structure, a graft structure and a star-shaped structure by combining a plurality of polymer chains, but there are not known techniques of accurately regulating a structure containing both a polyolefin component and a polar polymer component.
Under these circumstances, the present inventors made extensive study for developing polymers which are excellent in productivity, contain a plurality of polyolefin components consisting of various α-olefin homopolymers or copolymers or a plurality of polar polymer components consisting of various polar monomer homopolymers or copolymers in one molecule, and can cover a broad molecular-weight range, and as a result, they found that a macroinitiator, a macromonomer and a reactive polymer, which are obtained by introducing functional groups into polyolefin, can be combined with polar monomers or their various polymers i.e. polar polymers and polymerized or reacted with one another to give a novel multi-branched polymer having a block structure/graft structure/star-shaped structure whose polymer structure is three-dimensionally regulated, and the present invention was thereby completed.